We found a highly significant main effect of stimulus modality on PSE shifts (Monkey M: β = 31.07, t (44) = 10.22, p = 3.412 × 10 −13 ; Monkey P: β = 6.044, t (44) = 8.457, p = 3.394 × 10 −9 ), as well as moderate evidence for an interaction between stimulus modality and self-motion amplitude (Monkey M: β = 733.5, t (44) = 3.016, p = 4.248 × 10 −3 ; Monkey P: β = 67.78, t (28) = 2.371, p = 0.02487).
The main effect of object distance on PSE shifts was modest, with a weakly significant dependence in only one subject (Monkey P: β = 4.851, t (28) = 2.253, p = 0.03225; Monkey M: t (28) = 0.1150, p = 0.9093), and no significant interactive effect of object distance and self-motion amplitude for either animal (Monkey M: t (28) = 1.746, p = 0.09163; Monkey P: t (28) = –0.6561, p = 0.5171).
There was a significant interaction between horizontal location and amplitude (Monkey M: β = 3,295.4, t (294) = 4.4066, p = 1.473 × 10 −5 ; Monkey P: β = 437.0, t (194) = 2.950, p = 3.576 × 10 −3 ), and the interaction between vertical location and amplitude was either significant or approaching significance (Monkey M: β = 1,356, t (294) = 1.814, p = 0.07077; Monkey P: β = 787.24, t (194) = 5.313, p = 2.966 × 10 −7 ).
In one subject, there was also a strong interaction between horizontal location and self-motion amplitude (Monkey P: β = 1,295, t (74) = 5.202, p = 1.780 × 10 −6 ), whereas this interaction only approached significance in the other subject (Monkey M: β = 2,508, t (114) = 1.707, p = 0.09055).